Intake system of internal combustion engine and method of controlling the intake system

An intake system of an internal combustion engine, comprising:

• a surge tank disposed on the upstream side of individual intake paths that are connected to and communicate with respective cylinders of the engine;
• a vacuum tank that is connected to and communicates with the surge tank, the vacuum tank being formed integrally with or separately from the surge tank;
• a valve that is selectively placed in a first position for communicating the vacuum tank with the surge tank and in a second position for inhibiting communication between the vacuum tank and the surge tank;
• and
• a control unit that controls opening and closing operations of the valve, wherein the control unit executes the steps of:
• opening the valve to place the valve in the first position when the surge tank is held in a negative-pressure condition during operation of the engine, and closing the valve to place the valve in the second position after a predetermined period of time has elapsed so as to hold the vacuum tank in a negative-pressure condition;
• opening the valve to place the valve in the first position for a predetermined period of time when a condition for starting the engine is satisfied, so as to reduce a pressure in the surge tank;
• and
• closing the valve when the engine is started.